1. Field of the Invention
This invention relates to a pulley block which can be advantageously used to string or exchange an aerial line.
When an aerial line, such as an overhead electrical conductor, grid, or signal line is exchanged with a new one, or when an aerial line is newly strung between outdoor towers or poles, a so-called pulley block method in which pulley blocks are hung from a rope is widely used.
2. Description of the Related Art
In the pulley block method, which will be discussed in detail hereinafter, a plurality of pulley blocks are hung from a rope at an appropriate distance to feed a new line therethrough. The rope is loosened or tensed to run the pulley blocks upside down.
In the pulley block method of the prior art, however, the pulley blocks are not always turned in the same direction, due to a torsion which the rope and/or the line (conductor) has, or to the wind which blows the line in course of stringing or exchanging operation when the pulley blocks are inverted, thus resulting in a decrease of the efficiency of the operation.